Upgraded to Ultimate & still can't join a domain!!!

Upgraded my Home Premium to Ultimate & cannot join my Win2k3 AD
Domain!!!
I can sit here & use my XP laptop & join no problem, but this Ultimate
piece of..... well, it just won't join!
I feel its a name resolution issue between this computer & DC,
although I have run dcdiag on my DC & everything passes.
When trying to join just using domainname, I am prompted for a
username & password for someone with permission to join the domain,
but eventually get the message:
An attempt to resolve the name of a DC in the domain being joined has
failed. Please verify that this client is configured to reach a DNS
server that can resolve DNS names in the target domain.
Oddly enough, I have to add the ISPs DNS servers to be able to get on
the internet, too.
Every XP box can join domain & browse the Internet using my internal
DNS server, though!
After callin M$ & routed to about 4 diferent people, II was told that
the call would cost $250!
I have been searching the intrnet & tried ump-teen different 'fixes'
that people have posted, as well.
HELP!!!